Method for producing aqueous preparations of complexes of platinum group metals

ABSTRACT

The invention relates to a method for producing aqueous preparations of complexes of platinum group metals (PGM) Pt, Pd, Rh and Ir having the general formula [M A /M B /M C  (L) a  (H 2 O) b  (O 2− ) c (OH − ) d ](OH—) e (H + ) f , wherein M A =Pt II  or Pd II , M B =Pt IV , M C =Rh or Ir, L is a neutral monodentate or bidentate donor ligand, and a is an integer between 1 and 4 (or 2) and/or between 1 and 6 (or 3), b is an integer between 0 and 3 (or 5), c is an integer between 0 and 3 (or 4), d is an integer between 0 and 3 (or 5), e is an integer between 0 and 2 (or 3 or 4) and f is an integer between 0 and 4 (or 5). In the method according to the invention, the hydroxo complexes H 2 P d (OH) 4  (in the case of M A =Pd II ), H 2 Pt(OH) 6  (in the case of M A =Pt II  and M B =Pt IV ) or H 3 M C (OH) 6  (for M C =Rh III  Ir III ) are converted in the presence of the donor ligands, wherein at least one hydroxo group of the hydro complex is exchanged. Preferably, the reaction occurs at temperatures in the range of 40 to 110° C. with a reaction time of between 2 and 24 hours, wherein, where MA=PtII, the conversion additionally occurs in the presence of a reduction agent. The method optionally further comprises an exchange of OH anions bound outside of the complex sphere with other anions (e.g. hydrogen carbonate or carbonate anions). The aqueous preparations contain PGM complexes such as [Pt(en) 2 ](OH) 2 , [Pt(EA) 4 ](OH) 2  or [Rh(NH 3 ) 6 ](OH) 3  and are used to produce electroplating baths, heterogeneous catalysts or metal powders, for example.

The present invention relates to a process for preparingwater-containing compounds and complexes of the platinum group metalsand also preparations, solutions and downstream products thereof. Thewater-containing preparations of the platinum group metal complexesproduced by the process are low in halogens and are used, for example,as noble metal components in electroplating baths and also as precursorsfor producing heterogeneous catalysts, for example automobile exhaustgas catalysts or supported catalysts.

For the purposes of the present patent application, platinum groupmetals (hereinafter referred to as “PGM” for short) are the metals ofthe second and third series of transition group 8 of the Periodic Tableof the Elements (PTE), i.e. the metals ruthenium (Ru), rhodium (Rh),palladium (Pd), osmium (Os), iridium (Ir) and platinum (Pt). Theinvention preferably relates to the compounds of the platinum groupmetals platinum (Pt), palladium (Pd), rhodium (Rh) and iridium (Ir). Forthe purposes of the present patent application, “PGM-ammine complexes”are complexes of the platinum group metals with ammonia ligands (NH₃ligands). Such complexes are sometimes also referred to as “ammoniates”.Examples are hexaamminerhodium(III) trichloride [Rh(NH₃)₆]Cl₃ ortetraammineplatinum(II) dichloride [Pt(NH₃)₄]Cl₂.

The designation “PGM-amine complexes” is used collectively for complexesof the platinum group metals with amino, alkylamino, dialkylamino,hydroxyalkylamino and alkoxyamino ligands. The term preferably refers tothe ligands ethylenediamine (abbreviated to “en” in the present patentapplication) and 2-aminoethanol (ethanolamine, abbreviated to “EA” inthe present patent application).

Many of the simple and commercially available PGM compounds, for examplepalladium chloride (PdCl₂), hexachloroplatinic acid (H₂PtCl₆), or amminecompounds of the platinum group metals, e.g. Pt(NH₃)₄Cl₂, containhalides, in particular chloride ions. Chloridic solutions or solids ofthe PGMs typically represent the industrial starting materials for thepreparation of the corresponding higher-value compounds. Thesechloride-containing solutions or solids are obtained by dissolution ofthe pure noble metals or else as products of noble metal recyclingprocesses. The PGM-containing products (for example supported catalystsor electroplating baths) produced using these compounds are contaminatedwith chloride residues, which is undesirable for, inter alia, corrosionreasons. Thus, for example, chloride-containing noble metal baths inelectroplating technology attack the plant material. Catalysts which areproduced using chloride-containing precursors can likewise have acorrosive action and display reduced activity and also a shortened life.

In addition, it is known that chlorine-containing PGM salts, inparticular chlorine-containing Pt salts, are hazardous to health andcan, for example, trigger allergies; they are therefore undesirable forreasons of occupational hygiene.

In the following, the designation “low-halide” or “low-chloride” or“low-chlorine” refers to a total halogen value or total chlorine contentof <5000 ppm, preferably <2000 ppm (measurement by, for example, theWickbold method, based on the respective metal content of thepreparation). The halogens encompass the group fluorine, chlorine,bromine and iodine, and the term halides is used to refer to thecorresponding anions F⁻, Cl⁻, Br⁻ and I⁻.

For the abovementioned reasons, the search for suitable, commerciallyattractive low-halogen compounds or preparations of the platinum groupmetals is an important field of work in industrial noble metalchemistry. Even though many low-halogen compounds, for example thenitrates or sulfates of the platinum group metals, e.g. platinumnitrate, rhodium nitrate, palladium sulfate, and also more complexsubstances such as [(NH₃)₄Pd](HCO₃)₂ are commercially available, thesearch for new substances is a field of work being continuously pursued.

PRIOR ART

Many of the PGM compounds which are halogen-free according to theirformula still have high residual halogen contents which result from theproduction process thereof and can be reduced only by complicated andthus expensive processes, e.g. ion exchange processes. Varioushalogen-free PGM compounds can be prepared only by means of such ionexchange processes. This applies particularly to compounds of platinumand rhodium; in the case of palladium, the chlorine-free compoundspalladium nitrate and palladium sulfate are directly accessible asaqueous solutions.

Thus, EP 512,960 A1 and U.S. Pat. No. 5,244,647 disclose a process forpreparing low-chlorine hexaamminerhodium(III) trihydroxide[Rh(NH₃)₆](OH)₃ and tetraammineplatinum(II) dihydroxide [Pt(NH₃)₄](OH)₂,which uses a process involving ion exchangers for removing the chlorideions. Here, the compounds [Rh(NH₃)₆]Cl₃ or [Pt(NH₃)₄]Cl₂ are used asstarting materials. The compound [Rh(en)₃](OH)₃ is also known and hasthe CAS No. 198292-46-5. However, the preparation of this compound isnot described.

DD 288065 describes a process for preparing puretetraamminepalladium(II) dihydrogencarbonate [Pd(NH₃)₄](HCO₃)₂, in whicha [Pd(NH₃)₄]X₂ complex (X═Cl⁻, NO₃ ⁻) is reacted with a cation exchangerand an ammonium hydrogencarbonate solution.

Further examples for low-chlorine (or low-chloride) PGM compounds aretetraaammineplatinum(II) dihydrogencarbonate [Pt(NH₃)₄](HCO₃)₂,tetraammineplatinum(II) diacetate [Pt(NH₃)₄](CH₃COO)₂,tetraammineplatinum(II) dinitrate [Pt(NH₃)₄](NO₃)₂ ortetraamminepalladium(II) diacetate [Pd(NH₃)₄](CH₃COO)₂. Here, thechlorine-free salt solutions are each case obtained from thecorresponding hydrogen carbonates (solids) in multistage processes.

EP 2,116,550 B1 describes a method of preparing chlorine-free complexesof palladium(II) hydrogencarbonate with amine ligands, in whichtetraamminepalladium(II) dihydrogencarbonate [Pd(NH₃)₄](HCO₃)₂ isreacted with an organic amine ligand with removal of the ammonia. Theprocess has a number of stages and is very time-consuming since it takesa relatively long time for the ammonia to have been completely drivenoff.

A. Syamal and B. K. Gupta (Transition Met. Chem. 8, 280-282, 1983)describe the preparation of square planar platinum(II) complexes withN-containing chelating ligands and oxygen-containing ligands (e.g.oxalate or acetate). The latter are datively bound directly to thecentral Pt(II) atom, i.e. they are within the coordination sphere of thecentral Pt(II) atom. The preparation of such complexes (for examplePt(II)(NH₂C₂H₄OH)(CH₃COO)₂) starts out from chlorine-containingcompounds such as K₂PtCl₄. The complexes described by Syamal and Guptadiffer in terms of their structure from the Pt(II) complexes of thepresent invention; since chlorine-containing compounds are also used asstarting materials in the preparation, complicated methods of removingthe chloride ions are also necessary here.

Conventional halogen-free PGM compounds, for example the nitrates orsulfates of the platinum group metals, have sulfur or nitrogen atomswhich in a pyrolysis reaction liberate environmentally polluting sulfuroxides or nitrogen oxides. For this reason, preference is given to PGMprecursor compounds which on heating undergo a residue-freedecomposition and do not have any N atoms or S atoms. In summary, thelow-halogen PGM compounds mentioned are generally expensive because oftheir multistage preparative processes and the complicated purificationsteps (e.g. ion exchange processes) and are not very feasible asstarting materials for industrial processes.

It is therefore an object of the present invention to provide aneconomical and inexpensive process for preparing low-halogen, inparticular low-chlorine, PGM compounds and water-containing preparationsand solutions thereof. These preparations or solutions should have a pHin the range from weakly acidic to basic. Furthermore, preparationswhich contain hitherto unknown PGM complexes should be made available.

This object is achieved by provision of the process as claimed in theaccompanying claims. Furthermore, novel PGM-containing preparationswhich can be obtained by means of process of the invention are provided.

SUMMARY OF THE INVENTION

The invention relates to a process for producing water-containingpreparations of compounds and complexes of the platinum group metals(PGM), in particular the metals platinum (Pt), palladium (Pd), rhodium(Rh) and iridium (Ir). The invention encompasses essentially threeembodiments.

In a first embodiment, the invention provides a process for producingwater-containing preparations of complexes of the platinum group metals(PGM) having the general formula (1)

[M^(A)(L)_(a)(H₂O)_(b)(O²⁻)_(c)(OH⁻)_(d)](OH⁻)_(e)(H⁺)_(f)  (1)

where

-   -   M^(A)=platinum (Pt) or palladium (Pd) in the oxidation state +2        and    -   L=an uncharged monodentate or bidentate donor ligand and    -   a=an integer from 1 to 4 (for monodentate donor ligands) or an        integer from 1 to 2 (for bidentate donor ligands),    -   b=an integer from 0 to 3,    -   c=an integer from 0 to 3,    -   d=an integer from 0 to 3,    -   e=an integer from 0 to 2 and    -   f=an integer from 0 to 4        and the platinum group metal M^(A) has the coordination number        4,        which process is characterized in that the hydroxo complexes        H₂Pd^(II)(OH)₄ (in the case of M^(A)=Pd) or H₂Pt^(IV)(OH)₆ (in        the case of M^(A)=Pt) are in each case reacted with an uncharged        donor ligand L, where at least one hydroxo group of the hydroxo        complex concerned is replaced and in the case of M^(A)=Pt the        reaction is carried out in the presence of a reducing agent.

In a further embodiment, the invention provides a process for producingwater-containing preparations of complexes of the platinum group metals(PGM) having the general formula (2)

[M^(B)(L)_(a)(H₂O)_(b)(O²⁻)_(c)(OH⁻)_(d)](OH⁻)_(e)(H⁺)_(f)  (2)

where

-   -   M^(B)=platinum (Pt) in the oxidation state +4 and    -   L=an uncharged monodentate or bidentate donor ligand and    -   a=an integer from 1 to 6 (for monodentate donor ligands) or an        integer from 1 to 3 (for bidentate donor ligands),    -   b=an integer from 0 to 5,    -   c=an integer from 0 to 4,    -   d=an integer from 0 to 5,    -   e=an integer from 0 to 4 and    -   f=an integer from 0 to 4        and the platinum group metal M^(B) has the coordination number        6,        which process is characterized in that the hydroxo complex        H₂Pt^(IV)(OH)₆ is reacted with an uncharged donor ligand L,        where at least one hydroxo group of the hydroxo complex is        replaced. Here, the reaction is carried out without addition of        a reducing agent.

In a third embodiment, the invention provides a process for producingwater-containing preparations of complexes of the platinum group metals(PGM) having the general formula (3)

[M^(C)(L)_(a)(H₂O)_(b)(O²⁻)_(c)(OH⁻)_(d)](OH⁻)_(e)(H⁺)_(f)  (3)

where

-   -   M^(C)=rhodium (Rh) or iridium (Ir) in the oxidation state +3 and    -   L=an uncharged monodentate or bidentate donor ligand and    -   a=an integer from 1 to 6 (for monodentate donor ligands) or an        integer from 1 to 3 (for bidentate donor ligands),    -   b=an integer from 0 to 5,    -   c=an integer from 0 to 4,    -   d=an integer from 0 to 5,    -   e=an integer from 0 to 3 and    -   f=an integer from 0 to 5        and the platinum group metal M^(C) has the coordination number        6,        which process is characterized in that a hydroxo complex of the        type H₃M^(C)(OH)₆ is reacted with an uncharged donor ligand L,        where at least one hydroxo group of the hydroxo complex is        replaced.

The indices a-f in the general formulae (1), (2) and (3) are selected sothat the resulting PGM complexes are electrically neutral.

In all three embodiments of the invention, the reaction is generallycarried out at a reaction temperature in the range from 40 to 110° C.and over a reaction time in the range from 2 to 24 hours. Preference isgiven to a reaction temperature in the range from 45 to 100° C. and areaction time in the range from 2.5 to 20 hours.

The above-described water-containing PGM-containing preparations aregenerally aqueous solutions; the reactions are preferably carried out inwater as solvent. However, the water-containing preparations can alsocontain organic, preferably water-miscible, solvents, for examplealiphatic alcohols (for example ethanol, isopropanol, butanol, etc.)and/or aliphatic ketones (for example acetone, methyl ethyl ketone,etc.). In these cases, the reaction can also be carried out in suchwater-containing solvent mixtures.

In the three different embodiments of the process of the invention, theligand replacement of the OH groups in the hydroxo complexes H₂Pd(OH)₄,H₂Pt^(IV)(OH)₆ or H₃M^(C)(OH)₆ (in the case of M^(C)=Rh^(III) orIr^(III)) by the uncharged donor ligands L does not have to be complete,so that mixed complexes can also be present. These can also have aquoligands (=uncharged H₂O ligands, number b), oxo ligands (O²⁻ ligands,number c) and hydroxo ligands (OH⁻ ligands, number d) in addition to theuncharged donor ligands L (number a). The electrical neutrality of theresulting PGM complex is achieved by further hydroxo radicals of thetype (OH⁻, number e) which are located outside the complexation sphere.These hydroxo radicals will be referred to as “hydroxy groups” or“hydroxide groups” in the present patent application. In the case ofresulting PGM complexes having an overall anionic charge, the presenceof protons (H⁺, number f) has to be taken into account in order toensure electrical neutrality.

The preparations of the invention contain PGM complexes which in thecase of complete hydroxo group replacement are generally cationicallycharged, and in the case of partial replacement and/or the presence ofoxo or hydroxo ligands are also anionically charged or uncharged. Thewater-containing preparations of the invention are thus in many casesmulticomponent mixtures of anionic, cationic or uncharged complexes.

However, in all embodiments of the process of the invention, thereplacement of at least one hydroxo group of the respective hydroxocomplex by an uncharged donor ligand L occurs, as a result of which, forexample, the solubility of the resulting PGM hydroxo complex in water isbrought about. The coordination numbers (CN) for monodentate ligands,namely 4 (for M^(A)=Pt^(II) and Pd^(II), general formula (1)) and 6 (forM^(B)=Pt^(IV), general formula (2)) and for M^(C)=Rh^(III) or Ir^(III),general formula (3), are in principle maintained in the complexes of theinvention. This applies analogously when bidentate ligands are used.

DETAILED DESCRIPTION OF THE INVENTION

The process of the invention is described in more detail below. Thepresent process in principle starts out from the low-halogen hydroxocomplexes of the platinum group elements. In the case of Pt, Pd, Rh andIr, these are, for example, the starting compounds H₂Pt(OH)₆(“hexahydroxoplatinic(IV) acid”), H₂Pd(OH)₄, H₃Rh(OH)₆ and H₃Ir(OH)₆.These compounds are prepared in various processes known to those skilledin the art by reaction of the respective chlorine-containing startingsalts with alkalis such as NaOH, KOH or ammonia in aqueous solution andoptionally subsequent neutralization. The best results are obtained whenfreshly prepared or precipitated hydroxo complexes (cf. examples) areused. In another notation, H₂Pt(OH)₆ is written as Pt(OH)₄×2 H₂O,H₂Pd(OH)₄ is written as Pd(OH)₂×2 H₂O, H₃Rh(OH)₆ is written as Rh(OH)₃×3H₂O and H₃Ir(OH)₆ is written as Ir(OH)₃×3 H₂O. Here too, these aregenerally complex mixtures of substances; however, the differentnotations are inconsequential to the essence of the present invention.

The hydroxo complexes or hydroxides of the PGMs are generally sparinglysoluble in water and can thus easily be separated off and washed bycustomary methods until they have a low halide content. In the case ofH₂Pt(OH)₆, residual contents of chlorine of <5000 ppm, preferably <2000ppm (in each case based on the metal Pt) are achieved. These complexesare thus suitable starting materials for the process of the inventionfor preparing low-halide PGM compounds. The residual chlorine content ofthe PGM compounds prepared by the present process can be set via thechlorine content of the hydroxo starting complexes.

It is known to those skilled in the art that in the reaction of thePt-hydroxo complex H₂Pt(OH)₆ with ligands such as ammonia orethanolamine, the cationic H⁺ ion is normally replaced and the six-foldOH coordination on the Pt atom is retained. Thus, for example, thereaction of H₂Pt(OH)₆ with ammonia or ethanolamine in aqueous solutionunder mild conditions forms the corresponding ammonium salts ofhexahydroxyplatinic acid, cf. eq. (a) and (b):

H₂Pt(OH)₆+2 NH₃=>(NH₄)₂[Pt(OH)]₆  (a)

H₂Pt(OH)₆+2 HO—C₂H₄—NH₂=>(HO—C₂H₄—NH₃)₂[Pt(OH)]₆  (b)

In these cases, the ligand sphere of the platinum is not changed. ThePGM is present in an anionic (i.e. negatively charged) hexacoordinatedhydroxo complex.

It has now surprisingly been found that under particular reactionconditions the reaction proceeds differently and the ligand L enters thecoordination sphere of the PGM hydroxo compound and direct ligandexchange with the complexed OH ligands thus occurs. This is all the moresurprising because the PGM hydroxides have hitherto been considered bythose skilled in the art to be insoluble in ammonia (the PGM hydroxidescan, inter alia, also be prepared and isolated by precipitation withammonia).

The reactions according to the invention can be illustrated by way ofexample by the following equations (where in each case complete ligandexchange is shown).

a) In the case of complexes of the type [M^(A)(L)_(a)(H₂O)_(b))O²⁻)_(c)(OH⁻)_(d)](OH⁻)_(e)(H⁺)_(f):

for M^(A)=Pd(II), a=4, b=0; c=0; d=0; e=2, f=0:

Ligand exchange: H₂[Pd^(II)(OH)₄]+4 L=>[Pd^(II) L₄](OH)₂+2 H₂O  (c)

for M^(A)=Pt(II), a=4, b=0; c=0; d=0; e=2, f=0:

Reduction: H₂Pt^(IV)(OH)₆+2e ⁻+2 H⁺=>H₄Pt^(II)(OH)₆=>H₂[Pt^(II)(OH)₄]+2H₂O  (d1)

Ligand exchange: H₂[Pt^(II)(OH)₄]+4 L=>[Pt^(II) L₄](OH)₂+2 H₂O  (d2)

Here, L in eq. (c) and (d2) is in each case an uncharged, monodentatedonor ligand. When a bidentate ligand L (for example en) is used, a=2.As reducing agents in eq. (d1), preference is given to using theresidue-free reducing agents described further below.

b) In the case of complexes of the type [M^(B) (L)_(a) (H₂O)_(b)(O²⁻)_(c) (OH⁻)_(d)](OH⁻)_(e)(H⁺)_(f):

for M^(B)=Pt(IV), a=6, b=0, c=0, d=0, e=4, f=0:

Ligand exchange: H₂[Pt^(IV)(OH)₆]+6 L=>[Pt^(IV)L₆](OH)₄+2 H₂O  (d3)

c) In the case of complexes of the type [M^(C) (L)_(a) (H₂)_(b)(O²⁻)_(c) (OH⁻)_(d)](OH⁻)_(e)(H⁺)_(f):

for M^(C)=Rh(III) or Ir(III); a=6, b=0, c=0, d=0, e=3, f=0:

Ligand exchange: H₃[M^(C)(OH)]₆+6 L=>[M^(C)L₆](OH)₃+3 H₂O  (e)

Here, L in the equations (d3) and (e) is in each case an unchargedmonodentate donor ligand; when a bidentate ligand L (for example en) isused, a is accordingly 3.

It should be noted that the abovementioned reaction equations areformal, simplified reaction equations which serve as models and in whichcomplete replacement of the hydroxo groups is shown in each case.However, this is not always the case in practice. As indicated above,partial replacement of the hydroxo ligands is possible, especially sincethe products are present in aqueous solution. For this reason, not onlythe abovementioned uncharged donor ligands L but also other donorligands such as uncharged aquo ligands (H₂O) or oxo ligands (O²⁻) orhydroxo ligands can be coordinated to the central PGM. This can, forexample in the case of Rh(III), lead to mixes in which further,partially OH-substituted cationic complexes such as [Rh(NH₃)₅(OH)](OH)₂or [Rh(NH₃)₄(OH)₂](OH) (where a=4, b=0, c=0, d=2; e=1, f=0) are presentin addition to the main product [Rh(NH₃)₆](OH)₃ (a=6, e=3). However,overall uncharged complexes such as [Rh(NH₃)₃(OH)₃] or singly anioniccomplexes such as H[Rh(NH₃)₂(OH)₄]⁻ (where a=2, b=0, c=0, d=4; e=0, f=1)can also be formed (cf. example 5).

Furthermore, partially substituted aquo complexes in which the unchargeddonor ligands are partly replaced by H₂O molecules can also occur. Thiscan, for example in the case of Pt(IV), lead to mixes in which partiallysubstituted aquo complexes such as [Pt(NH₃)₅(H₂O)](OH)₄,[Pt(NH₃)₄(H₂O)₂](OH)₄ or [Pt(NH₃)₃(H₂O)₃](OH)₄ are present in additionto the main product [Pt(NH₃)₆](OH)₄. This also applies analogously tothe other platinum group metals of the invention described here.

However, for reasons of clarity and of simplification, completereplacement of the OH ligands in the PGM hydroxo complex concerned bythe uncharged donor ligand(s) L is generally assumed for the purposes ofthe present patent application and the main product formed thereby isindicated in each case.

In the reactions according to the invention, the abovementioned PGMcomplexes are generally dissolved or dispersed in deionized (DI) wateror in a water-containing solvent mixture and the ligand L is added.

The process of the present patent application makes a differentcoordination chemistry of the platinum group metals possible: in apreferred embodiment, it opens the door to low-halogen platinum(II) orpalladium(II) complexes and also to low-halogen rhodium(III) oriridium(III) complexes. In these compounds, the PGM can be present in acationic (=positively charged), uncharged or weakly anionic (=negativelycharged) complex. Should the anion be present as hydroxide anion (OH⁻)outside the complexation sphere, it can in this case be replaced byother anions in a further step. The process of the invention thereforein principle encompasses ligand exchange (in the case of M^(A)=Pt(II)accompanied by reduction), optionally followed by a further step inwhich the OH anion bound outside the complexation sphere is replaced byan alternative anion (hereinafter referred to as “anion exchange” forshort).

The individual steps of the process of the invention are explainedbelow.

a) Ligand Exchange

In the process of the invention, the ligand exchange (i.e. the reactionwith the donor ligand L) is carried out at elevated temperatures andover a prolonged period of time. The temperatures are in the range from40 to 110° C., preferably in the range from 45 to 100° C. The reactiontime is in the range from 2 to 24 hours, preferably in the range from2.5 to 20 hours. The reaction is preferably carried out in aqueoussolution, but, as mentioned above, it is also possible to use organicsolvents, e.g. aliphatic alcohols and/or aliphatic ketones, optionallyin a mixture with water.

In general, the ligand L is added in the respective stoichiometric ratioto the reaction mixture, but the ligand L can optionally also be addedin superstoichiometric amounts. This is, for example, the case forammonia (NH₃) in order to compensate for vaporization losses overprolonged reaction times.

Suitable ligands L are monodentate or bidentate, uncharged donor ligandswhich make available 2 electrons (in the case of monodentate ligands) or4 electrons (in the case of bidentate ligands) in each case.

As monodentate donor ligands, use is generally made of ligands from thegroup consisting of monoalkylamines, dialkylamines, trialkylamines,monoalkanolamines, dialkanolamines, trialkanolamines, monoarylamines,diarylamines, triarylamines, trialkylphosphines, triarylphosphines,trialkoxyphosphines, triaryloxyphosphines (triaryl phosphites) andmixtures thereof and ammonia. Examples of preferred monodentate ligandsare the nitrogen-containing ligands ammonia (NH₃), ethylamine,diethylamine, ethanolamine (“EA”) or isopropanolamine. Examples ofsuitable P-containing monodentate donor ligands are triphenylphosphine,tricyclohexylphosphine and phosphites such as triphenyl phosphite.

As bidentate donor ligands, use is made in each case of ligands from thegroup consisting of alkylenediamines, arylenediamines, alkylenediphosphines or arylenediphosphines and mixtures thereof. Examples ofpreferred bidentate ligands are ethylenediamine (“en”),o-phenylenediamine, trimethylenediamine, tetramethylenediamine,pentamethylenediamine, hexamethylenediamine or 1,2-propylenediamine. Anexample of a suitable bidentate P-containing ligand is1,2-bis(diphenylphosphino)ethane.

Tridentate or polydentate donor ligands can also be used analogously.Examples of tridentate ligands are diethylenetriamine(H₂N—CH₂—CH₂—NH—CH₂—CH₂—NH₂, DETA) or dipropylenetriamine. Examples ofpolydentate ligands are trimethylenetetramine or hexamethylenetetramine.The numerical values of the parameter a should be adapted appropriately.Mixtures of the abovementioned ligands are also possible.

Particular preference is given to using nitrogen-containing monodentateor bidentate donor ligands. Very particular preference is given to usingthe ligands ammonia (NH₃), ethanolamine (“EA”), ethylenediamine (“en”)or mixtures thereof. Examples of water-containing preparations accordingto the invention prepared by ligand exchange are preparations whichcontain complexes having the following composition as main product:

-   for M^(A)=Pd(II): [Pd(NH₃)₄](OH)₂, [Pd(en)₂](OH)₂-   for M^(B)=Pt(IV): [Pt(EA)₆](OH)₄-   for M^(C)=Rh(III), Ir (III): [Rh(NH₃)₆](OH)₃, [Rh(en)₃](OH)₃,    [Ir(en)₃](OH)₃

b) Reduction

A specific case is the preparation of low-halide Pt(II) compounds.According to the invention, the Pt-hydroxo complex in the oxidationstate +IV (i.e. H₂Pt^(IV)(OH)₆) is used as starting material and isreacted with the ligand L in the presence of a reducing agent, with thetetravalent Pt(IV) being reduced to divalent Pt(II). The reducing agentssuitable for this purpose are known to those skilled in the art;preference is given to using “residue-free” reducing agents, i.e. oneswhich after the reduction reaction leave behind no residues or onlysmall residues in the product solution and generally do not have to beseparated off. Examples of such “residue-free” reducing agents arehydrogen (H₂) and hydrogen-comprising mixtures such as N₂/H₂ 80/20 or95/5; also hydrazine (N₂H₄), formaldehyde (HCHO), oxalic acid (H₂C₂O₄)or formic acid (HCOOH). To reduce Pt(IV) to Pt(II), the reducing agentis added in the redox equivalent ratio of from 1:1 to 2:1 (based on Pt).Preference is given to using equivalent amounts of reducing agent, andthe addition is generally carried out simultaneously with the additionof the ligand(s) in aqueous solution.

Examples of such preparations according to the invention prepared byligand exchange and simultaneous reduction are preparations whichcontain Pt(II) complexes having the following composition as mainproduct:

[Pt(en)₂](OH)₂,[Pt(NH₃)₄](OH)₂,[Pt(EA)₄](OH)₂

c) Anion Exchange

The process of the invention can also comprise replacement of thehydroxy anions of the type (OH⁻)_(e) in the complexes of the generalformulae

[M^(A)(L)_(a)(H₂O)_(b)(O²⁻)_(c)(OH⁻)_(d)](OH⁻)_(e)(H⁺)_(f)  (1)

[M^(B)(L)_(a)(H₂O)_(b)(O²⁻)_(c)(OH⁻)_(d)](OH⁻)_(e)(H⁺)_(f)  (2)

[M^(C)(L)_(a)(H₂O)_(b)(O²⁻)_(c)(OH⁻)_(d)](OH⁻)_(e)(H⁺)_(f)  (3)

by one or more anions of inorganic or organic acids. In the indicatedformulae (1), (2) and (3), the meanings of M^(A), M^(B), M^(C), L, a, b,c, d, e and f are as defined above in the previous sections. In thisanion exchange, a neutralization, i.e. a replacement of the hydroxyanions (OH⁻)_(e) by the appropriate acid anions, takes place inprinciple, and water is formed. To carry out the anion exchange,cationic complexes in which index e≠0 should be present. e is preferablyan integer from 1 to 4, particularly preferably 2, 3 or 4, and f ispreferably 0.

Suitable acids are, for example, acetic acid (CH₃COOH), formic acid,oxalic acid (H₂C₂O₄) or carbonic acid (or carbonates andhydrogencarbonates), or else sulfuric acid, phosphoric acid,tetrafluoroboric acid (HBF₄) or nitric acid. As anions of inorganic ororganic acids, it is possible to use anions from the group consisting ofacetates, formates, oxalates, carbonates, hydrogencarbonates, sulfates,nitrates, phosphates, tetrafluoroborates and mixtures thereof.

It is advantageous to react equimolar amounts of these acids with thebasic PGM-hydroxy complexes in an aqueous or water-containing solutionor preparation. The reaction temperatures are generally in the rangefrom 25 to 100° C., and suitable reaction times are in the range from 30minutes to 3 hours. This gives low-halogen, acidic to neutral PGMcompounds which are generally present in an aqueous solution orpreparation and are processed further in this form.

In the case of the hydroxy compounds of the type [M^(A)(L)_(a)](OH)₂(M^(A)=Pt^(II), Pd^(II), b=c=d=f=0, e=2) as an example, this anionexchange can be represented schematically by the equation (f):

[M^(A)(L)_(a)](OH)₂+2 H⁺X⁻=>[M^(A)(L)_(a)]²⁺X₂+2 H₂O  (f)

Here, X⁻ is a singly negatively charged acid anion, for example HCO₃ ⁻,CH₃COO⁻, HCOO⁻ or NO₃ ⁻. In the case of doubly negatively charged anionsY²⁻ (for example CO₃ ²⁻, C₂O₄ ²⁻, SO₄ ²⁻), the anion exchange can berepresented according to equation (g):

[M^(A)(L)_(a)](OH)₂+(H⁺)₂Y²⁻=>[M^(A)(L)_(a)]²⁺Y+2H₂O  (g)

In the case of the PGM-hydroxy compounds of the type[M^(B)(L)_(a)]⁴⁺(OH)₄ (M^(B)=Pt^(IV), b=c=d=f=0, e=4) and[M^(C)(L)_(a)]³⁺(OH)₃ (M^(C)=Rh, Ir, b=c=d=f=0, e=3), too, and alsocorrespondingly for triply negatively charged anions such as PO₄ ³⁻, theanion exchange proceeds analogously.

Examples of such water-containing preparations according to theinvention produced via anion exchange are preparations which containcomplexes having the following composition as main product:

-   for M^(A)=Pd(II): [Pd(NH₃)₄](HCO₃)₂,[Pd(en)₂](CH₃COO)₂,    [Pd(NH₃)₄]SO₄-   for M^(B)=Pt(II): [Pt(en)₂](CO₃),[Pt(EA)₄](C₂O₄),[Pt(EA)₄](CH₃COO)₂    -   [Pt(NH₃)₄](HCO₃)₂, [Pt(EA)₄]CO₃, [Pt(EA)₄](HCO₃)₂-   for M^(B)=Rh(III) [Rh(NH₃)₆](CH₃COO)₃-   for M^(B)=Ir(III) [Ir(NH₃)₆](PO₄)₃

Characterization of the Complexes

The compounds and complexes of the present invention are in most casesmixtures in which variously coordinated PGM complexes are presentside-by-side in a water-containing or aqueous preparation or solution.The concentration of the respective PGM (Pt, Pd, Rh or Ir) is in therange from 0.5 to 15% by weight (based on the total weight of thepreparation or solution).

The low-halogen water-containing or aqueous preparations, mixtures orsolutions according to the invention generally have a weakly acidic tobasic pH. Thus, the pH of the water-containing preparations of theinvention is in the range pH 5 to 14, preferably in the range pH 7 to 14and particularly preferably in the range pH 7 to 12.

The characterization of the preparations or solutions and complexes iscarried out by conventional analytical methods such as capillaryelectrophoresis; the determination of the Pt, Pd, Rh or Ir content canbe carried out by means of ICP (“inductively coupled plasma”) or bygravimetric methods.

¹⁹⁵Pt-NMR Spectroscopy

The coordination sphere of the PGM complexes of the invention can in thecase of platinum be determined by means of ¹⁹⁵Pt-NMR spectroscopy. Themeasurements are carried out using a BRUKER AVANCE 400 (from BrukerBioSpin GmbH, Rheinstetten, DE); H₂PtCl₆ in D₂O is used as externalreference (δ=0 ppm), and a DMSO capillary is used as “locking solvent”.The chemical shifts of the Pt(II) complexes of the invention are in therange from δ=−2000 to −3200 ppm. In the [Pt(NH₃)₄](OH)₂ solutionprepared according to the invention, it is possible to confirm, forexample, the existence of the square planar [Pt(NH₃)₄]²⁺ cation by meansof the signal at δ=−2576 ppm.

Determination of the Chlorine Content

The chlorine content of the PGM-containing preparations of the inventionis typically in the range <5000 ppm, preferably <2000 ppm (totalchlorine content, based on the respective PGM content). Thedetermination of the chlorine content is carried out by a method whichcomprises the steps: (1) taking-up of the sample in a suitable solvent,(2) combustion in an H₂/O₂ flame, (3) collection of the condensate insodium hydroxide solution and (4) determination of the chlorine contentby ion chromatography (IC). This method is known as “total chlorineanalysis by the Wickbold method”. However, other, equivalent methods canalso be used.

The water-containing, PGM-containing preparations or solutions areemployed in many fields of use. They can be used as PGM precursors, forexample in electroplating baths or for producing homogeneous orheterogeneous catalysts. Furthermore, they can be used for producinghigh-purity PGM-containing powders and for the preparation of furthercomplexes. For the purposes of the present invention, the expression“further complexes” refers to complexes which are different from thecomplexes used in the respective reaction. This can be brought about,for example, by reduction, oxidation, ligand exchange on the complexesused or combinations thereof. Oxidations and reductions of the complexesused also encompasses reactions in which only the respective metal atomor only one or more ligands change their oxidation number or oxidationstate. The water-containing preparations obtained by the process of thepresent patent application can thus undergo a reaction to obtain furtherproducts, for example electroplating baths, homogeneous or heterogeneouscatalysts, metal powders or further complexes. In addition to or insteadof a reaction, formulation of the water-containing preparations obtainedby the process of the present patent application can also take place,including, inter alia, addition of further constituents, for example ofauxiliaries or solvents, replacement of constituents, for example thesolvent, and/or the removal of constituents, e.g. the removal ofby-products or unreacted starting materials, but also solvents. Theremoval of solvents can also be carried out in order to formulate thepreparation so as to increase, for example, the concentration of theother constituents.

The following examples illustrate the invention in more detail butwithout restricting the scope of protection thereof.

General Preliminary Remarks

The reactions described below are carried out under an air atmosphereusing deionized water (DI water) as solvent. In general, glass flasksprovided with reflux condenser and dropping funnel are used.

The PGM hydroxo complexes H₂Pt(OH)₆ or Pt(OH)₄×2 H₂O)(“hexahydroxoplatinic(IV) acid”), H₂Pd(OH)₄ or Pd(OH)₂×2 H₂O, H₃Rh(OH)₆or Rh(OH)₃×3 H₂O and H₃Ir(OH)₆ or Ir(OH)₃×3 H₂O are generally freshlyprepared before the respective reaction. For this purpose, thehydroxides are precipitated from chloridic solution by means of alkalimetal/alkaline earth metal hydroxide or ammonia, separated off andwashed to a low halide content with DI water. The appropriate methodsand sequences of operations are known to a person skilled in the fieldof noble metal chemistry.

Example 1 (Tetraammine)Platinum(II) Hydroxide Solution

5 g of Pt (25.6 mmol) as H₂Pt(OH)₆ (freshly precipitated, manufacturerUmicore AG & Co KG, Hanau) are placed together with 150 g of 25%strength ammonia solution and 100 ml of DI water in a glass flaskprovided with reflux condenser and heated. At a temperature of 40° C.,1.19 g of formic acid (25.6 mmol) diluted in 50 ml of water are added.The reaction mixture is heated (T=70-80° C.) overnight (about 16 hours).A clear, colorless solution containing small amounts of fully reducedplatinum as grey solid is formed. Analysis of the clear supernatantsolution indicates a content of 1.58% by weight of Pt; this correspondsto a yield of 92% (based on the Pt used). The [Pt^(II)(NH₃)₄]²⁺ cationis identified in the solution prepared by means of capillaryelectrophoresis (signal at a retention time of from 2 to 2.5 minutes).

Furthermore, the existence of the [Pt(NH₃)₄]²⁺ cation is confirmed bymeans of ¹⁹⁵Pt-NMR spectroscopy (chemical shift at δ=−2576 ppm). Thetotal chlorine content of the aqueous (tetraammine)platinum(II)hydroxide solution is 560 ppm based on platinum (Wickbold method).

Example 2 Bis(Ethylenediamine)Platinum(II) Hydroxide Solution

5 g (25.6 mmol) of Pt as H₂Pt(OH)₆ (manufacturer Umicore AG & Co KG,Hanau) are placed together with 3.08 ml (51.2 mmol) of ethylenediamine(for synthesis, Merck) and 100 ml of DI water in a glass flask providedwith reflux condenser and heated while stirring. At 60° C., 1.19 g offormic acid (25.6 mmol) diluted in 50 ml of water are added via adropping funnel. The reaction mixture is heated at 75° C. overnight(about 15 hours). A yellow-orange solution is formed. The Pt content ofthe solution is 0.58% by weight, corresponding to a yield of 32% of theplatinum used.

Example 3 (Tetraammine)Palladium(II) Hydroxide Solution

10.0 g (0.094 mol) of palladium in the form of 41 g of freshlyprecipitated moist palladium hydroxide (Pd(OH)₂×2 H₂O; manufacturerUmicore AG & Co KG, Hanau) which has been washed free of chloride areintroduced into a tiered 250 ml three-necked flask and made up with DIwater to a total amount of 50 g. 35.5 ml of 25% strength ammoniasolution are added while stirring. The solution is subsequently heatedto 65° C. under reflux while stirring and maintained at this temperaturefor 2.5 hours. The solution formed is cooled to room temperature (about23° C.), admixed with 0.2 g of activated carbon (Norit SC) and stirredat room temperature for one hour. The mixture is filtered through a blueband filter and washed with 10 ml of DI water. This gives 87.2 g of ayellow-orange solution. The solution contains 11.13% by weight of Pd.This corresponds to a yield of 97.05% based on palladium used. The totalchlorine content of the solution is 809 ppm (based on Pd).

Capillary electrophoresis proves the presence of the [Pd(NH₃)₄]²⁺ cationby cross-comparison with Pd(NH₃)₄ compounds which were prepared by aconventional method (i.e. main signal at a retention time of 2.5minutes).

Example 4 Bis(Ethylenediamine)Palladium(II) Hydroxide Solution

10.0 g (0.093 mol) of palladium in the form of about 37 g of freshlyprecipitated moist palladium hydroxide (Pd(OH)₂×2 H₂O; manufacturerUmicore AG & Co KG, Hanau) which has been washed free of chloride areplaced in a tiered three-neck flask and made up with DI water to a totalmass of 70 g. The three-necked flask is provided with a refluxcondenser, the reaction mixture is stirred by means of a magneticstirrer and the temperature is controlled by means of an oil bath. Theoil bath temperature is about 23° C. 11.2 g of ethylenediamine (0.186mol; for synthesis, Merck) are mixed with 12.4 g of DI water in a glassbeaker and cooled to a temperature of about 18-20° C. (water/ice bath).

The aqueous ethylenediamine solution is added all at once to the stirredpalladium hydroxide suspension. The reaction mixture is heated for 18hours by setting of an oil bath temperature of 45° C. while stirring.The resulting yellow-orange, largely clear solution is cooled to roomtemperature (about 23° C.). 0.5 g of activated carbon (Norit SC, NoritDeutschland GmbH) is subsequently added and the mixture is stirred atroom temperature for 1 hour. The solid is subsequently filtered off on ablue band filter. The reaction flask is rinsed with 10 ml of DI waterand this water is filtered through the blue band filter with activatedcarbon and added to the product solution. This gives 98.7 g of a clearyellow solution. The solution contains 9.94% by weight of Pd. Thiscorresponds to a yield of 98.1% based on palladium used. The totalchlorine content of the solution is 804 ppm based on palladium.

Example 5 (Hexaammine)Rhodium(III) Hydroxide Solution

9.92 g of rhodium (0.0964 mol) in the form of about 31.4 g of moist,freshly precipitated rhodium hydroxide (H₃Rh(OH)₆ or Rh(OH)₃×3 H₂O,manufacturer Umicore AG & Co KG, Hanau) which has been washed to a lowhalide content are admixed in a 250 ml three-neck flask with DI water sothat the total weight of the suspension in the flask is 75 g. The flaskis provided with a magnetic stirrer and reflux condenser and 44 ml of25% strength ammonia solution (corresponding to 11 g of NH₃=0.65 mol) isadded all at once at room temperature while stirring. The mixture isheated while stirring to an internal temperature of 75° C. and thesolution is heated at this temperature for 20 hours. The reactionmixture is subsequently cooled to room temperature (about 23° C.) bymeans of a water/ice bath and admixed with 0.5 g of activated carbon(Norit SC). The mixture is stirred at room temperature for 1 hour andsubsequently filtered through a blue band filter. The reaction flask isrinsed with 10 ml of DI water and this is added via the filter to thereaction mixture. 116.1 g of a clear orange solution result. Thesolution contains 8.34% by weight of Rh. This corresponds to a yield of97.6% based on rhodium used. The total chlorine content of the solutionis 1210 ppm (based on Rh).

Capillary electrophoresis shows three signals; a signal (1) in theweakly anionic region, a small signal (2) at the neutral point and amedium strength signal (3) in the cationic region. This indicates aproduct mixture in which some hydroxo ligands have been replaced by NH₃,but not completely. Apart from the target compound [Rh(NH₃)₆](OH)₃(signal (3)), the uncharged partially substituted complex[Rh(NH₃)₃(OH)₃](signal (2)) can be present. The signal position of theanionic complex (1) indicates only a small negative charge and can beassigned to the complex H[Rh(NH₃)₂(OH)₄]⁻.

Example 6 Tris(Ethylenediamine)Rhodium(III) Hydroxide Solution

200 g of rhodium (1.94 mol) in the form of 711.7 g of moist, freshlyprecipitated rhodium hydroxide (H₃Rh(OH)₆ or Rh(OH)₃×3 H₂O, manufacturerUmicore AG & Co KG, Hanau) which has been washed to a low halide contentare admixed in a tiered 2 l three-neck flask with DI water so that thetotal weight of the suspension in the flask is 1000 g. The flask isprovided with a precision glass stirrer and reflux condenser and 350.5 g(5.82 mol) of ethylenediamine (for synthesis, Merck) are added all atonce while stirring at room temperature. The reaction mixture is heatedwhile stirring by application of an oil bath temperature of 60° C. Theoil bath temperature is slowly increased to 90° C. over a period of 3hours. From about 74° C., a slightly exothermic reaction is observed andthe solid begins to dissolve. After 3 hours, the reaction mixture iscooled to room temperature (about 23° C.) by means of a water/ice bathand admixed with 5 g of activated carbon (Norit SC). The reactionmixture is stirred at room temperature for 1 hour and subsequentlyfiltered through a blue band filter. The reaction flask is rinsed with100 ml of DI water and this is added via the filter to the reactionmixture. 1814.4 g of a clear orange solution result. The solutioncontains 11.0% by weight of Rh. An Rh-based isolated yield of 99.8% isthus obtained. The total chlorine content of the solution is 910 ppm(based on rhodium).

Capillary electrophoresis shows two cationic signals which can beassigned to the compounds [Rh(en)₃](OH)₃ (main signal) and[Rh(en)₂(OH)₂]OH (weak signal).

Example 7 Tris(Ethylenediamine)Rhodium(III) Acetate Solution

5.06 g of rhodium (49.2 mmol) in the form of 50.0 g of(trisethylenediamine)rhodium(III) hydroxide solution (about 10% byweight of Rh, prepared as described in example 6) are weighed into a 100ml three-neck flask. While stirring, 10.58 ml of 100% strength aceticacid are slowly added dropwise at room temperature (about 23° C.) untila pH of 7 has been reached. The dropwise addition time is about 30minutes; gentle evolution of heat occurs. The Rh content of the clearyellow solution obtained is 8.2% by weight.

1.-30. (canceled)
 31. A precursor for electroplating baths, forproducing heterogeneous catalysts or metal powders or for preparingfurther complexes which comprises the water-containing preparationsproduced by a process producing water-containing preparations ofcomplexes of the platinum group metals (PGM) having the general formula(1), (2) or (3)[M^(A)(L)_(a)(H₂O)_(b)(O²⁻)_(c)(OH⁻)_(d)](OH⁻)_(e)(H⁺)_(f)  (1) whereM^(A) platinum (Pt) or palladium (Pd) in the oxidation state +2 and L anuncharged monodentate or bidentate donor ligand and a an integer from 1to 4 for monodentate donor ligands or an integer from 1 to 2 forbidentate donor ligands, b an integer from 0 to 3, c an integer from 0to 3, d an integer from 0 to 3, e an integer from 0 to 2 and f aninteger from 0 to 4 and the platinum group metal M^(A) has thecoordination number 4, wherein the hydroxo complexes H₂Pd(OH)₄ in thecase of M^(A)=Pd or H₂Pt(OH)₆ in the case of M^(A)=Pt are in each casereacted with an uncharged donor ligand L, where at least one hydroxogroup of the hydroxo complex concerned is replaced and in the case ofM^(A)=Pt the reaction is carried out in the presence of a reducing agentor[M^(B)(L)_(a2)(H₂O)_(b2)(O²⁻)_(c2)(OH⁻)_(d2)](OH⁻)_(e2)(H⁺)_(f2)  (2)where M^(B) platinum (Pt) in the oxidation state +4 and L an unchargedmonodentate or bidentate donor ligand and a2 an integer from 1 to 6 formonodentate donor ligands or an integer from 1 to 3 for bidentate donorligands, b2 an integer from 0 to 5, c2 an integer from 0 to 4, d2 aninteger from 0 to 5, e2 an integer from 0 to 4 and f2 an integer from 0to 4 and the platinum group metal M^(B) has the coordination number 6,wherein the hydroxo complex H₂Pt(OH)₆ is reacted with an uncharged donorligand L, where at least one hydroxo group of the hydroxo complex isreplaced or[M^(C)(L)_(a3)(H₂O)_(b3)(O²⁻)_(c3)(OH⁻)_(d3)](OH⁻)_(e3)(H⁺)_(f3)  (3)where M^(C) rhodium (Rh) or iridium (Ir) in the oxidation state +3 and Lan uncharged monodentate or bidentate donor ligand and a3 an integerfrom 1 to 6 for monodentate donor ligands or an integer from 1 to 3 forbidentate donor ligands, b3 an integer from 0 to 5, c3 an integer from 0to 4, d3 an integer from 0 to 5, e 3 an integer from 0 to 3 and f 3 aninteger from 0 to 5 and the platinum group metal M^(C) has thecoordination number 6, wherein a hydroxo complex of the typeH₃M^(C)(OH)₆ is reacted with an uncharged donor ligand L, where at leastone hydroxo group of the hydroxo complex is replaced.
 32. The precursoras claimed in claim 31, wherein the indices a-f in the general formulae(1), (2) and (3) are selected so that the PGM complexes are electricallyneutral.
 33. The precursor as claimed in claim 31, wherein themonodentate donor ligands is ammonia or ligands selected from the groupconsisting of monoalkylamines, dialkylamines, trialkylamines,monoalkanolamines, dialkanolamines, trialkanolamines, monoarylamines,diarylamines, triarylamines, trialkylphosphines, triarylphosphines,trialkoxyphosphines, triaryloxyphosphines and mixtures thereof.
 34. Theprecursor as claimed in claim 31, wherein the nitrogen-containingligands ammonia, ethanolamine, ethylamine, diethylamine,isopropanolamine or mixtures thereof are used as monodentate donorligands.
 35. The precursor as claimed in claim 31, wherein thenitrogen-containing ligands ethylenediamine, o-phenylenediamine,trimethylenediamine, tetramethylenediamine, pentamethylenediamine,hexamethylenediamine, 1,2-propylenediamine or mixtures thereof are usedas bidentate donor ligands.
 36. The precursor as claimed in claim 31,wherein the replacement of the OH groups in the hydroxo complexesH₂Pd(OH)₄, H₂Pt(OH)₆ or H₃M^(C)(OH)₆ in the case of M^(C)=Rh^(III) orIr^(III) by the uncharged donor ligands L is incomplete and theresulting compounds of the general formulae (1), (2) or (3) continue tocontain aquo (H₂O), oxo (O²⁻) or hydroxo (OH⁻) ligands.
 37. Theprecursor as claimed in claim 31, wherein hydrogen, an H₂/N₂ mixture,hydrazine (N₂H₄), oxalic acid (H₂C₂O₄), formaldehyde (HCHO) or formicacid (HCOOH) or mixtures thereof are used as reducing agent in the caseof M^(A)=platinum(II).
 38. The precursor as claimed in claim 31, whereinthe water-containing preparations contain organic solvents.
 39. Theprecursor as claimed in claim 31, wherein the concentration of theplatinum group metals M^(A), M^(B) or M^(C) in the water-containingpreparation is in the range from 0.5 to 15% by weight.